text:
What is the maximum altitude of barometric altimeters?
An altimeter works by sensing static air pressure. As altitude goes up, the pressure decreases.
If I take a barometric altimeter up to space (e.g. up to satellite orbit), at what altitude does its reading become useless, i.e. the reading can no longer be trusted as a measurement of the height above sea level?
(While altimeter reading is different than GPS altitude even at low altitudes, it is still a very good measurement of height. I'm asking at what height, the air becomes so thin that it is implausible to measure altitude based on static air pressure?).

Most altimeters are impossible to interpret altitude above 100,000 feet because the littlest hand (10k indicator) makes one complete revolution. I'm guessing the answer may be at some point below vacuum where there just isn't enough  molecules of air to affect the diaphragm, it may be manufacturer specific.

The SR-71 manual describes what seems like a normal altimeter and  mentions an altitude correction card that was used with the altimeter. Since they flew at the 100,000'+ level, presumably an altimeter would work at least that high. http://sr-71.org/blackbird/manual/1/1-136.php

The Smithsonian has an altimeter that NASA had planned to use with the Gemini missions. It could measure altitudes up to 80,000'. https://airandspace.si.edu/collection-objects/altimeter-barometric

The max altitude will depend on the instrument and the installation.  I suspect it's safe to say that the max reliable altitude is a lot higher in a system installed in something like an SR-71 or U-2 than in a C-150 or the like, but it's hard to get the Cessna up to 80,000' to see just how far off the altimeter actually is up there!

@RalphJ My Cessna and Cherokee have been tested on the bench and certified by the avionics shop to 20,000'. I’m guessing that the SR-71 has some sort of testing similar to what my avionics shop does.

Found this set of pictures of the cockpit of an SR-71. http://atomictoasters.com/2012/07/the-forward-cockpit-of-sr-71-977/ Looks like the altimeter can go to 100,000'. I haven’t been able to find documentation on its accuracy at that altitude.

Note: I am focusing on model of height-to-pressure relation in atmosphere, altimeter tries to follow and its limits of the model. There are, of course, limits of each particular instrument too, see answer by @ymb1.
[EDIT: I have added more details on various uses of altitude and some more details what could be the limit for measuring absolute altitude (it is not how thin air becomes, in fact), hope it answers your question better.]
Uses for altimeter reading
Height displayed by common mechanical altimeter should be pressure converted according to the International Standard Atmosphere (ISA) model. This model makes few simplifications (see the linked document for ex.), so it actually never gives exact height, except by chance. But as you are saying, it is anyway quite good approximation.
When you are flying, there is few different reasons why you would need to look on altimeter.

Obstacle avoidance, landing and maybe calculating final glide in glider. In this case it is really absolute height over terrain you need to know. To get this value you have to start with obtaining QNH, so already now altimeter itself is not enough (in any altitude) without external data. For greater precision you have to add more external data. You start with local temperature, but even then precision would be limited.
The magnitude of error does not depend on your absolute altitude though, but (in first approximation) on height difference between airplane and station/place your QNH comes from. So you are lucky if you want to land. Given QNH comes from that particular airfield, your altimeter should read exact value just on touchdown. If you need to avoid obstacles at similar altitude, error will be likely acceptable for practical use.
Again, it is not absolute altitude but relative difference what is causing this error. If you set QNH (or runway altitude) on airfield located 4000' above sea level and fly down to the see (let's say it is possible without traveling far away, so spatial change of air pressure is not an issue here), expected error of your altimeter will be similar as if you would fly 4000 feet up. It is because QNH (pressure at the sea level) is calculated based on the same model your altimeter is using, so model imperfections cancels out just at the altitude of this reference station.
ATC, mid air collisions etc. Absolute altitude is not important.
Instead, you need to be sure that two pilots who see distinct values on their respective altimeters can expect not being at same altitude. For this purpose simplest model with minimum of external parameters works best. As it is of foremost importance that all altimeters involved converts pressure to height in the same way. (Then, you need to expect pressure does not increase with altitude, but this is quite certain, as there will be always less air mass above you pressing down when you go upwards). Absolute altitude is completely unimportant here, or, for flying closer to terrain simple QNH-based offset will do. (Otherwise STD pressure setting is used.)
Even simple altimeter (in range of its physical limits of measurable pressure) would work quite well for this purpose in any practical height.
Aircraft performance and aerodynamics. That is service ceiling, choosing optimal cruise etc. These parameters are usually denoted in altitude in a POH, but only for convenience. It is air density what matters for anything aerodynamic related. And air density is air pressure corrected to temperature. So "altitude" provided by pressure-based altimeter is "just right" for this purpose, you can correct it based on local temperature and you have the best possible value. Again, this will work in any height (as long as POH and altimeter use same conversion between pressure and height).

Note that for later two uses value provided by altimeter is actually better than, say, GPS-based height.
Absolute altitude
OK, what if you really want to know your absolute altitude in stratosphere or even higher. Is it possible to use your altimeter then?
If the altimeter converts pressure to height based on ISA (true in most cases), the displayed value should be given by equation
$$
h=\left(153.85\,{\rm m\cdot K^{-1}}\right)\cdot T_0 \cdot \left(1-\left(p\over p_0\right)^{0.19026}\right)
$$
(see the reference above), where $T_0$ is specified to be 288.15 K (15 °C)
 and $p_0$ is pressure you set in altimeter window. So, if you take such altimeter to space ($p=0$) it won't display more than 44 km (or 145,000 feet), given it won't reach it's physical/mechanical limits before. But, of course, the value becomes far from reality much earlier. Probably above the tropopause (10–12 km), where assumption of constant temperature decrease with height used in this ISA model becomes completely invalid. You could improve the model, but it probably won't work too well without more external data.
Nevertheless, problem is not that the air is thin. You can, in a way, measure air pressure even at low earth orbit few hundreds kilometer above ground. It is just the atmosphere what imposes (measurable) drag on satellites in low orbits. So yes, there is still something to measure and it is for sure measurable with right instrument. Problem is that you do not have any practical and "dependable" way how to calculate height based on this local pressure (only). Many other effects comes in play and you would need to know many other variable parameters in order to calculate altitude.
But, well, it was so already from beginning, wasn't it? You had to obtain right QNH (external info) even if you would fly in traffic pattern only. So the situation with altimeter at the orbit is not so much different actually.

While flying, you actually do not need to know your absolute altitude in many practical situations and pressure-based altimeter works perfectly regardless of height. If you need to know your exact altitude the limit is not air being to thin, but rather distance from closest station which can provide reference pressure.
With meteorological balloon located close to your aircraft and sending "QNH" for you (based on local pressure balloon measures and its known height, analogically to QNH coming from an airport), you could have quite good reading from (suitable) pressure-based altimeter even high in the stratosphere for example.

10-12km is well within the cruise altitude of most jets...

ISA/US Standards Atmosphere 1976 is still used in digital altimeters above the tropopause altitude, which simply requires a different calculation

@ronBeyer, although that's true, jets operating at those altitudes have 2 things going for them; 1: they no longer need to know their absolute height since the flight levels are pressure levels and not altitudes; and, 2: at 10-12km, aircraft are (most likely*) RVSM-certified, meaning that their altimeters are specially-certified and are coupled with air data computers to give a more accurate reading.  (non-RVSM aircraft must stay below FL290 [roughly 8km] because their altimeters are not as accurate).  *note: non-RVSM aircraft may get special exemption to fly above FL290.

@selectstriker2, not sure if different calculation only is enough. Tropopause is not located at fixed altitude and other conditions are quite variable too, so you will need more external data to calculate useful altitude value, won't you? But I have no practical experience here (only theory), so feel free to correct me if I am wrong.

ISA and US Standard Atmosphere 1976 both use a constant for the Tropopause altitutide - 11,000m or 36,089 ft.

TSO C10B Altimeter, Pressure Actuated, Sensitive Type uses SAE AS 392C to specify minimum requirements for a pressure altimeter. It specifies two "types" of pressure altimeters

Type 1: Range 35,000 ft
Type 2: Range 50,000 ft

AS392C also provides the tolerances a pressure altimeter must meet from -1000 ft to 50,000 ft.
TSO C106 Air Data Computer also provides some minimum performance requirements for an air data computer providing pressure altitude. It provides tolerances from 0 ft to 50,000 ft.
This is why you'll see high altitude pressure altimeters end around the 50,000 ft to 60,000 ft mark, as calibrating digital pressure sensors for higher altitudes becomes difficult and very few planes need altimeters certified to more than 50-60,000 ft.


text:
How high can I fly a kite above my farm?
This idea is inspired by this question.
Suppose the OP decides to fly some kites or helium balloons above his farm to keep other pilots from flying near it. Regulation-wise, how high can these objects go?

Crop dusters hit unmarked obstructions less than 200' pretty regularly, usually ending pretty badly for the pilot. I wouldn't want to be responsible for a kite or balloon killing a pilot, even if it were legal to fly it.

It depends how big the balloon or kite is. Balloons and kites are governed by 14 CFR 101, but specific regulations only apply above a certain size. 101.1 says:

a) This part prescribes rules governing the operation in the United
  States, of the following:
(1) Except as provided for in §101.7, any balloon that is moored to
  the surface of the earth or an object thereon and that has a diameter
  of more than 6 feet or a gas capacity of more than 115 cubic feet.
(2) Except as provided for in §101.7, any kite that weighs more than 5
  pounds and is intended to be flown at the end of a rope or cable.

However, note the reference to 101.7, which says (in part):

No person may operate any moored balloon, kite, amateur rocket, or
  unmanned free balloon in a manner that creates a hazard to other
  persons, or their property.

That means, if your balloon or kite is too small to be governed by part 101 then there are no specific restrictions on how you operate it, but you still can't fly it in a way that puts other people in danger.
If part 101 does apply to you, then you have to follow the rules in 101.13 and 101.15:

§101.13   Operating limitations. (a) Except as provided in paragraph (b) of this section, no person may operate a moored balloon
  or kite—
(1) Less than 500 feet from the base of any cloud;
(2) More than 500 feet above the surface of the earth;
(3) From an area where the ground visibility is less than three miles;
  or
(4) Within five miles of the boundary of any airport.
(b) Paragraph (a) of this section does not apply to the operation of a
  balloon or kite below the top of any structure and within 250 feet of
  it, if that shielded operation does not obscure any lighting on the
  structure.
§101.15   Notice requirements. No person may operate an unshielded moored balloon or kite more than 150 feet above the surface of the
  earth unless, at least 24 hours before beginning the operation, he
  gives the following information to the FAA ATC facility that is
  nearest to the place of intended operation: [contact details, time, altitude etc.]

There are more requirements in 101.17 and 101.19.

As the Internet is a World wide communication medium, it should be noted what country's rules are being quoted. In Australia the rules for recreation aviation activities is governed by CASA (Civil Aviation Safety Authority). The general rule is 120 metres or 400 ft. AGL. and not within 5 km of airports and requires apecial approval with a zone and conditions assigned. 400 ft. is nearly out of sight for a small kite and is a pain to wind that much line in for a child. Adults may fly bigger kites and they may occasionally exceed these limits and brag about it on forums. They often don't know the regulations or don't care. Generally flying a kite at 500 or 600 ft. doesn't cause problems to air traffic as long as it's not near an airport. The normal low level cruise for light aircraft is 1,500 ft. so it is not that easy to a fly a kite that high and consequently I would say it is very rare that a pilot would encounter a kite. People seem to fly kites almost exclusively at kite festivals or the beach these days. I know these things because my team captured the World Record of 16,009 ft. in 2014.

"400 ft. is nearly out of site for a small kite and is a pain to wind that much line in for a child"  I can confirm a more extreme case.  I had a kite on an 1800 foot nylon string, then added another roll, and then another.  That made it about a mile.  I had no idea where the kite was, and it took almost forever to reel back down.  By the time I got home, the pressure of all those string windings had crushed my reel, breaking its 1 inch wooden dowels.  And of course at that age it never occurred to me that I might be endangering anyone.

Welcome to aviation.SE! To your point on which country this is about, the question was posted with the faa-regulations tag, i.e. the US regulations. If you're new to the site, the [tour] might be helpful to see how tags and other features work.

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text:
Can pilots identify tail strike from the cockpit?
Is there any system, on board, that can warn pilots that a tail strike happened?

Other than, presumably, a palpable bang that shakes the whole plane?

Related: What is the purpose of the Dash 8’s “TOUCHED RUNWAY” warning light?

@DarthPseudonym There's also value in detecting a tailstrike has not occurred. More than one turnback has happened because shifting luggage caused a good thump during rotation.

@DarthPseudonym Depends. Sometimes a tail strike cannot even be felt in the cockpit.

Large aircraft have a tail contact sensor. On the A350, this sensor contains two independent electric loops which are broken when the contact occurs. This condition is reported to the crew using the MASTER CAUT (master caution) lights, an ECAM message and a chime as explained in this AAIB Bulletin:

When a tailstrike does occur, the two wires in the sensor are damaged and become open circuit from their normally grounded (GND) state. The change of signal state is detected by the Common Remote Data Concentrators which change the format of the data and transmits it to the Flight Warning System (FWS) via the Avionics Full Duplex
Switched Ethernet (AFDX).

The FWS shows a warning on the ECAM Warning Display providing the aircraft is in the appropriate flight phase, landing or taking off.

A single chime is also produced from the flight deck loudspeakers. On the cockpit glare shield and panels 411VU and 412VU, MASTER CAUT push buttons are also illuminated (Figure 8).

Other than an ECAM message, the system warnings are inhibited when TOGA is selected during landing.

A similar system exists on Boeing 787 (Dreamliner, see AAIB report):

Tail contact sensor on a Boeing 787. Source.
It seems older large aircraft, like Airbus A320 or Boeing 737, had sensors unable to trigger an alert. A light tail contact would be felt only by flight attendants at the rear of the cabin.
Remarks:

The flight control computers are assumed to prevent the contact to occur in the first place, by monitoring the pitch attitude, however for some reason, like after a bounce at landing, heavy cargo sliding in the rear bay, or wind gust, the aircraft may over-rotate without crew action and too fast for the protection to work.

A tail contact occurs within periods of sterile cockpit, FA must anyway report the contact without delay to the pilots. A tail contact affects first a non-pressurized area of the aircraft, but the pressure vessel may have been damaged too, preventing a safe pressurization, and a fire can also occur in the non-pressurized tail cone where the APU is usually located. A landing is required as soon as possible, and a limited altitude must be maintained.

See also:

 Why are so many tail-strike incidents not verified until later inspection?

 How do manufacturers engineer their aircraft to deal with tail strikes?

 What is the purpose of the Dash 8’s “TOUCHED RUNWAY” warning light? (identified earlier by Bianfable)

Airbus Safety First: A320 Tail strike at Take-Off?

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text:
What would happen when a pilot receives a message about Dead Reckoning Fault?
Dead Reckoning Fault will lead to some restrictions of the flight. What will happen after receiving this message?

In what aircraft?

In any aircraft! Airbus, Boeing and etc.

How would this message be sent:ECAM/EFIS, ..? and why? Could you point to some documentation, or tell us what you know about this message?

It would be sent by ECAM or on the panel.

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text:
What would happen if the Emergency Locator Transmitter was activated wrongly?
Supposing, after a "bad" landing, performing a high vertical speeed, the crew, unintentionally, activates the ELT, sending the signs to the sattelites, warning the rescue and team about the "accident", that does not happen.
Would the fees for the services be payed?
Is there any penalty for the crew or company?

On a similar note, I had a few friends who found out that an ELT they were looking for was accidentally activated on a boat.

There was a bizarre thing a few years ago where a TV set was emitting an ELT signal. They didn't charge the guy or the company, but he had to leave it off until the TV company replaced it. Apparently normal electronics do this on a somewhat regular basis

It happens ALL the time. I have been on many airport hunts looking for the airplane with a triggered ELT. You tale a handheld radio and walk through the ramp until you find it.

The ELT guys get a lot of false alarms. About 97% of ELT alerts are false alarms. Most false alarms are generated by bad ELTs on boats.
Neverthless, they chase them all down. The organization that does this is the Civil Air Patrol.
Legally, a person activating false alarm can be held liable for substantial fines, but in practice it is unknown for those fines to be assessed for an accidental alert. If someone was deliberately setting off an ELT, the FCC might attempt to prosecute and assess a fine, which by statute can be as much as $100,000.

The organization that chases down ELT activations is the US Coast Guard, assisted by the US Air Force through the Civil Air Patrol. See AC 91-44A. You can also activate an ELT during the first 5 minutes of the hour (and for 3 sweeps) for testing purposes, or at any time if arranged with the nearest tower or FSS.

@RonBeyer The CAP always finds the transmitter first. Who they call after they find it depends on where it is.

And source for the 97% claim?

Unintentionally activation of ELT ,,1 when more than 1/2 of battery life time is passed .2 when You move ELT without putting its switch to off position , When you use a big ferromagnetic device neat to ELT , when you leave for a long time the Aircraft in a hanger without switching off or removing ELT from Aircraft , in case of unintentionally activation of ELT contact immediately the nearest ATC and inform them . Your Sincerely Rajabi 28th Nov 3022

Hi, and welcome. This answer is barely intelligible and doesn't seem to answer the question ("what would happen...?") or add any insight not already given in existing answers.

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.


text:
What's the difference between 'Go Around' and 'Pull Up'?
We use on the standard RT (radio telephony) Go Around. But what's the difference between Go Around and Pull Up?

RT = radio telephony (communication between ATCos and Pilots)

Going around is a process, pulling up is an action. When ATC tells you to go around or you say you are going around it means you are initiating a set of actions to abort an approach. Pulling up is a single action, i.e. increasing the angle of attack in order to climb, and would be part of a go-around procedure.
Pull up is a non-standard phrase, in most parts of the world at least, but you might hear it as 'pull up and go around' in Canada. It also might be used in urgent situations to urge a pilot to act to avoid an obstacle or collision.

You might also hear "pull up" from Bitching Betty.

This is true @Devil07, but it's not used in RT typically.

@Devil07 But...not until after you've already ignored her warnings about your sink rate.

I may be overemphasizing an implicit part of your answer, but isn't "pull up and go around" misleading since the first thing a pilot does during go around is advance the throttle fully and gain speed before gaining altitude?  To me "pull up" sounds like you're try to gain altitude immediately, which in some cases is a fatal mistake.

I would completely agree @CodyP. Pull up and go around is an official phraseology in Canada, as shown in their RT documentation, unless that's changed in the past few years. Personally I don't like it but it's part of a complete answer.

@J..., not necessarily. “Sink rate” is only issued during approach, but “pull up” anytime you are getting dangerously close to the ground. So if you are flying level and there is rising ground ahead, you will hear just “terrain, terrain” and then shortly “terrain, pull up”.


text:
What's the difference between "rapid descent" and "emergency descent"?
The pilots should inform ATC when performing emergency descent, but, reporting a rapid descent, is it the same? Can you please, say some situations the pilots will report rapid descent?

Well, an emergency descent is one where you're descending for safety and a rapid descent is one where you expedite a normal descent procedure. Another example to help differentiate between the two is an explosive decompression. The crew would initiate an "emergency descent" but if they suspect airframe damage they may consider maintaining the current speed and aircraft config to avoid further damage.
Goal of Emergency Descent: The goal is to descend as quickly as possible while remaining within the aeroplane's structural limitations. Not always rapid, requires an active emergency posing a threat to operations.
Goal of Rapid Descent: Aircraft descends at a much steeper rate than during a normal descent. This is usually done to quickly reach a lower altitude during emergency procedures but not always.
You are not going to not report either of them, both terms are usually used interchangeably but are not normal procedures either.

Both are descents where you will do the following steps:

Thrust levers idle.
Autopilot to speed mode, and dial the speed bug to Vmo/Mmo, unless you suspect structural damage (such as from a frightening bang coming from the back), in which case you set the speed bug to current speed.
If you have in-flight deployable speed brakes/spoilers that are good to operate at Vmo/Mmo, fully out to increase the descent rate.

If it's an emergency, like a cabin pressurization warning or smoke, you will be donning masks, setting the transponder to 7700, and declaring an emergency on the radio, which allows you to start down immediately and will have ATC clear the decks for you on the way down. Plus you will dial the ALT select on the autopilot to 10000 ft so it captures the altitude when you get there.
If it's not an emergency and you don't mind waiting, you'll be requesting a clearance for lower, perhaps asking for priority and explaining why, and you will leave the masks alone, or only have one crew member don one as a precaution (you might do this if a windshield crack appears, which is not uncommon, is usually on the  outer lamination and benign, and you decide you don't need to go full ED but want to reduce pressure differential as fast as possible), and no transponder selection.
Also, if it's a non-emergency, you may avoid deploying flight spoilers/speed brakes or cranking up the speed to Vmo/Mmo, because the noise tends to scare the passengers.


text:
What are the engine-out implications of giant turbofans?
It seems that turbofans for civil airliners are improving fuel efficiency by building larger and larger fans that spin slower.  For example, the RR Trent 800 introduced in 1993 had a diameter of 2.8m, while the RR Trent Ultrafan expected in 2025 may be 3.56m in diameter.
In the case where both engines fail in flight, I imagine that wider engines would create much more drag, reducing glide distance.  Is this true, and if so, what do aircraft manufacturers and airlines do to mitigate it?

Trent 800 MTBF > 120 years! and Trent 1000 is 2 IFSD (in-flight shutdown) per million flight hours.

@mins, I was thinking of both engines failing because of a common cause, like volcanic ash, fuel exhaustion (Gimli glider scenario), or bird strikes (miracle-on-the-Hudson scenario).  Perhaps those cases play an inordinately large role in the public imagination.

The question is valid. Most cases of the last 40 years result from errors (lack of knowledge for ashes), except bird strikes, but for them considering the low height, the glide ratio difference is likely not very relevant. Still there are new surprising shutdown causes.

Both-engine-out glide performance isn't accounted for and isn't a certification requirement (of any airplane that I'm aware of).  Airliners have good glide performance as a happy side effect of design optimization for cruising at high altitudes.
What does have to be accounted for is single engine performance issues; things like departure performance with an engine failure at V1, single engine ceilings, etc.  Gliding ability comes into it in a secondary way, in terms of what is called "driftdown".  Driftdown is when you are forced to descend from a both engines cruising altitude to the single engine ceiling following an engine failure or shutdown when your power is cut in half, and  could be thought of as "semi-gliding" or "power assisted" gliding performance.
Driftdown speeds are speeds to use to get the flattest descent with maximum continuous thrust on the good engine, and you may use these speeds where terrain clearance means you need to stay at high as possible for as long as possible. Driftdown performance is measured during certification for the purpose of providing data for the pilots in the QRH, but there is no minimum driftdown "flatness" or glide ratio requirement per se.
As far as designing around geared TFs, well, the effects are what they are, and since nobody makes feathering fan blades, you are stuck with whatever the drag penalty is. A windmilling GTF is going to have more windmilling drag than a direct drive TF. But a direct drive TF has more windmilling drag than a traditional turbojet.  So what did the manufacturers do when TFs came out?
They made allowance for the differences, and maybe an airliner would need somewhat more thrust from a given engine in TF form, all else being equal, to accommodate the higher windmilling drag of a failed engine on the other side, compared to the same airplane with pure turbojets. The drag penalties are not as bad as windmilling propellers, and don't necessitate radical solutions like feathering fan blades.
Geared TFs just take the same problem a little farther, but still get away without needing things like feathering fans (which would have killed the entire GTF concept) by making sure the thrust reserve is there to deal with a windmilling fan.  But if a GTF equipped airplane ends up with a both-engines-out glide ratio of 12:1 instead or 14:1 because of the drag of its super-size fans, that's neither here nor there.

Maybe one more aspect: A failed GTF engine also causes some loss of lift on the wing and a yawing moment (due to asymmetric thrust and drag), which the tailplane must be able to counter, plus additional trim drag. In new aircraft designs, there's a balance between engine size, the distance between engines and fuselage and VTP size. The associated compromises are part of the technological "cost" of using GTF engines but usually much smaller than the efficiency benefit. In re-engined aircraft, it mostly just limits engine size. It also pushes research on improved nacelle designs :)

Also: note that the Rolls-Royce Ultrafan does include a variable-pitch rotor! It probably won't be able to be "feathered" in the same way a propeller can, but some pitch settings will create less windmill drag, and I'm sure there will be some mechanism to pitch it to "minimum windmill drag" whenever needed. That should lessen the impact of windmill scenarios quite a bit, too (although the "stuck rotor" scenario after a shaft or bearing failure might still remain...)


text:
How could a wood and fabric aircraft be controlled after a fabric tear mid-flight?
This question is specific to wood and fabric aircraft.
What would happen should the fabric for a wing tear mid-flight and what should the pilot do to increase his survivability following such an incident?
For the sake of the question, assume it's bird strike or similar that caused the tear, to one wing only, without any additional structural damage other than to tear the fabric.
I'm aware that for a large tear, the aircraft would spin out, and for a small tear it would have only a small effect(?), so I'm thinking specifically for a tear large enough to have a significant effect, but small enough that the pilot has a chance.
I've found very little about what to do following a fabric tear mid-flight. I found several AAIB reports - but these talk about the damage and what happened, not about what options the pilot had after whatever event caused the damage in the first place.

If you don't have enough aileron authority to control the roll, you may need to reduce the lift on the good wing to mitigate some of the effects. Perhaps a side-slip or forward slip might help. Rudder may have some rolling effect as well so it could be used. The problem is that you probably won't have much time to experiment before you corkscrew.

A wing tear is not something people train for because the impact on the airplane depends on where it is, how big it is, and what other systems have been damaged. If it's just a fabric tear then the damaged wing will produce less lift than the good one, meaning the airplane will want to roll in the direction of the damaged wing. For a pilot to survive there needs to be enough aileron and rudder authority to compensate for this and keep the plane level. So the first priority is to maintain positive control of the airplane and learn how to fly it again by using control inputs against the rolling action. If I feel like I need more aileron power I would decrease speed from cruise in small increments, seeing how a slower speed effects my ability to control the airplane, if it reduces the rolling and gives me better control then I'll keep decreasing speed bit by bit to find a sweet spot. If the damage happens at a slow speed, like in a climb, I would increase speed by increments. I would keep a very healthy margin above stall speed though, as the damage to the wing has probably increased the stall speed of the damaged wing. If the damaged wing stalls then I'm in a snap roll and unlikely to recover.
Once I have control I want to land as soon as I can, and I ideally want a very long runway into wind with emergency services. If I know the area well I probably already know where I want to go. If I can't maintain altitude then I need to find a big field, quick.
Once I've aviated an navigated I will communicate and declare an emergency with ATC and state my intentions. ATC can't help me fly the airplane so I didn't need them before now, but now they can help reduce my workload. If I don't know the area ATC can help me find the best place to go, and they can give me weather information and notify emergency services.
Once I get to an airfield comes the tricky part - landing. It's tricky because I don't know when the damaged wing is going to stall, so I have to keep a lot of extra airspeed on approach and landing without flaps (flaps will change the shape of the wing and the dynamics of the situation in ways I cannot anticipate). This means a faster approach and putting the wheels on the ground at a much faster speed - this is why I would want a really long strip. Once the wheels are on the ground if one wing stalls before the other I can probably control it, and the wheels will help give some stability as well while I gently brake.

I wondered about speed. There would be an instinctive drive to slow down because you'd be worried about further damage happening to the tear due to airflow, but also high enough speed to avoid a stall.
You sound like you're advising erring on the side of as fast as you can go while still maintaining control, would that be correct?

That's a good summary, yes. Ideally you'd slow down some to reduce further damage, but I'd do it slowly in increments.

@Dudley, no, as slow as you can go while maintaining control. Higher speed gives you more control authority, so at higher speed you will have less problems maintaining control.


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How to derive the Vortex line segment parallel to a plane using the Biot-Savart law?
I am trying to understand what is shown in this book (Applied hydro and aeromechanics), page 187
The velocity induced at a given point on a parallel plane by a vortex segment of length $b$, and strength $\Gamma$ is shown to be,
$v_1 = \frac{\Gamma b \, sin \, \alpha}{4 \pi R^2}$
Can anyone please show the steps on arriving this formula by applying Biot-Savart law ?

Please don't double post messages.

Meta post explaining why not to double post is here

I have answered this on physics.SE.


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How to calculate best glide speed at a 30 degree bank?
The Best Glide speed is the indicated airspeed that guarantees the maximum glide distance during an engine out scenario.  However, the landing straight ahead option after an engine failure may not be the best option especially if there is nothing but houses in front of you after an engine failure.  Sometimes turning back towards the field may be the best option.
The Best Glide speed is actually tied to a best Lift/Drag ratio for a specific angle of attack.  When in a banked turn, the pilot must increase the angle of attack to avoid a spiral dive.  So this implies that the best glide speed would increase during a banked turn in order to maintain the best L/D angle of attack.  My question is how would one calculate the Best Glide speed for an aircraft in a 30 degree bank based off the POH listed Best Glide at Gross Weight (I do realize best glide varies with weight).

This doesn't quite add up.  (A)  You say "When in a banked turn, the pilot must increase the angle of attack to avoid a spiral dive."  When gliding, why must the pilot increase the AoA?  Let's say you want to fly at the AoA for Min Sink Rate.  Isn't this the same AoA in wings-level flight as in a banked turn?  Same for stall AoA?  Same for best L/D AoA?  The concept of increasing AoA when banked pertains more to flying with a motor and trying to maintain a constant altitude.   (ctd)

I think your presumptions are incorrect.  When turning in an engine out glide you still want to maintain best glide speed, which will correlate to best L/D AOA.  However, in order to do so you will need to lower the nose, which will increase sink rate.

(ctd) Then you say (B)  "So this implies that the best glide speed would increase during a banked turn in order to maintain the best L/D angle of attack."  --yes, it must increase according to the square root of the change in wing loading .  So (B) is true.  But (B) doesn't follow logically from (A), because (A) is incorrect.

I think you can still fix this w/o invalidating the single answer posted so far, because the answer only addresses (B), not (A).

Another huge complication is that a 180 degree reversal arguably has nothing to do with best L/D at all.  You are in no sense trying to maximize forward distance covered.  You want to minimize time spent in the reversal and you also want to minimize the sink rate during the reversal.  I seem to recall I've seen analyses suggesting a 45-degree banked turn is the way to go, letting the airspeed bleed off (or even pulling the stick aft to help the airspeed bleed off) to near min sink for that bank angle -- but certainly not lower!-- I'd have to look some more to relocate those analyses--

@quietflyer I would like to see those analysis if you can did them up.  Perhaps I am thinking about this all wrong.  In the airplane world we are taught to maintain best glide when the engine goes out but I do understand that turns can be tighter when travelling at a slower speed.  Of course you will need to be careful not to stall the airplane which occurs at a high airspeed when banked.

During a turn the load factor increases. This increases the apparent weight. Thus, during a turn, the best glide speed is selected according to the weight times the load factor.
The load factor at 30 degrees bank is $$n=\frac{1}{\cos{\theta}} \approx 1.2$$
The best glide speed is thus the best glide speed for a weight that is 1.2 times your actual weight. This will be proportional to the square root of the load factor.
$$V_{opt,\theta}= \sqrt{\frac{1}{\cos{\theta}}} V_{opt,0^\circ}$$

Is this really correct? The load factor is only equal to 1/cos(theta) in level flight where you pull on the yoke to maintain altitude. But presumably one will not be attempting to maintain level flight during engine out.

@SMeznaric you are right about the level flight assumption being likely not valid during engine out conditions. However at small flight path angles, the formula approximates the load factor well. The correct form (assuming constant flight path angle or gamma) is cos(gamma)/cos(theta)

I am not sure that's correct @DeltaLina. If you're not pulling on the yoke and accept a higher descent rate during the turn then your load factor should stay unchanged.

@SMeznaric I am note sure what you are trying to achieve.  assuming coordinated flight, the load factor is directly related to the bank angle and the flight path angle.

I can't tell if your final equation is right or not, I am only taking an issue with your statement about the load factor going up in a turn. This is only true in level flight. And the reason it's true in level flight is because you need more lift to counteract gravity in a turn. But if you're not in level flight, you're trimmed out and turning without pulling, you'll increase your descent rate and then this assumption does not hold. The load factor in a turn in general could in general be higher or lower than the normal level flight load factor.

@SMeznaric no, it is not only true in level flight. Also in a flight of constant flight path angle this is true. Of course you can turn briefly with a load factor of 1, but you will accelerate downward during the turn. Very quickly you will develop an very negative vertical speed and thus loose a lot of altitude. Not what you want in an engine out scenario

You don't have many options in an engine out. If you're turning you'll have to increase your descent rate or lower your speed. If you lower your speed you're increasing your load factor and getting closer to a stall which in a stressful potentially uncoordinated turn might end up in spinning to the ground. Much preferable to turn without pulling and keep the airplane in the air.

I am not stating that you should not increase your descent rate. You will need to do that to maintain speed. Your speed should be as calculated above, and the descent rate adjusted accordingly. The load factor will be above 1, otherwise you will accelerate downward (meaning you will descent at an increasingly higher rate)

OK, so since your speed has gone up and your angle of attack is reduced, you accept then that the load factor going up to 1 / cos(theta) statement is not correct then? That's all I'm saying so it seems that we're on the same page.

Your speed has gone up, the angle of attack has stayed the same. The load factor has increased by a factor 1/cos(theta). In the transition into the turn, the load factor will be lower, but once established in the turn, cos(gamma)/(cos(theta) is the load factor.

If forces don't balance during the turn then your load factor can be anything independently of the angle of bank. But anyway, we're not getting anywhere, so I'll leave it here.

In a descending turn, maintain the same glide speed.  Your rate of descent will increase, but you can fly the same speed.
The issue of load factor in a banked turn applies to a level turn.  In a descent, fly your glide speed and let the descent rate increase.


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Where can I find the roster formats of various airlines?
I discovered a mobile app called roster minder for android. It seems that the app can import rosters from various airlines. I was wondering how that was possible? Is there a standard format for crew rosters or do airlines publish roster formats, which can be consumed by the app?

I know that there are third party applications that helps airlines create their rosters, so there would at least be identical formats between airlines that use the same program.

They likely import a calendar event format (e.g. iCalendar).


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What is the maximum number of planes a controller can control?
In a small and un-busy airport, the same controller can be the ground and tower at the same time. If the sector is un-busy (e.g. late at night), he may also be a sector, ground and tower all at the same time. At busy airports of course, ground and tower are two persons. Sometimes even ground is split to "Ground South" and "Ground North".
So there is a threshold where the communication has to be split into two, either because the frequency would be too busy (only one person can talk on the frequency at any time), or there are so many planes that a controller would start making mistakes.
What is that threshold? (Is it a concrete number, or some other conditions which can be objectively determined?)

ATC is slowly moving towards CPDLC to reduce vocal communications between aircraft controllers and pilots. The number of aircraft a controller will handle will blossom when it becomes widely implemented.... at least that's the FAAs hope.

@SteveH The "benefits" of CPDLC are pretty hotly contested, at least by the GA folks I know and the airline folks I listen to. (The loss of situational awareness from not having a "party line" frequency combined with the need to look away from the outside world or instruments to read text messages are pretty common issues that are raised.) - Might make an interesting question on its own, or a good subject to discuss in chat.

Are you asking about tower controllers (guys in a tower at an airport) or about ARTCC (managing wide area traffic)?

I'm mainly asking about tower controllers, but an answer addressing both would be helpful.

There is no fix maximum a controller is allowed to have under control, as the other answer already pointed out. The airspace under control of ATC is divided up into sectors containing the airways to and from airports within that sector or in upper sectors, airways just for en-route traffic. (see also: Why do pilots use airways instead of GPS direct?).
Sectors can be merged during off-peak hours, split back into separate sectors during peak hours and in the case of TMA or approach sectors, the controller owning the sector can receive additional help by splitting the approach sector further and using different controllers for different tasks within that sector: Feeder/Pickup - Director - Departure Controller. The thresholds of when a sector is split is dependent on many factors, like weather, runway in use, outside influences like adjacent sectors having more traffic that usual, special occurances within that sector like parachute jumper drops.
Sectors also vary in size and capacity based on their intended use. While TMA/Approach sectors are rather small and need to accomodate arriving traffic into an airfield, an enroute or upper sector can be significantly larger in size, lateral and vertical. Again, this is individual to each sector, because some factors which hold true for TMA sectors do not apply to enroute upper sectors and vice versa. It also really depends on the controller working the sector and his personal limits, favorite procedures and work practice. A few examples:

A TMA controller using vectors to the approach instead of standard arrival routes or transitions will have more workload to monitor and sequence aircraft.
The minimum radar separation in TMA sectors and upper sectors can be either 3NM or 5NM. While upper sectors are larger in size, they have to maintain a greater separation, so in some cases, an upper sector twice or multiple times the size of a TMA sector will only be able to accomodate the same number of aircraft (ceteris paribus) before reaching saturation.
A controller having to work with special situations such as aircraft in distress or student pilots requiring more attention than experienced pilots, will reduce the controllers personal capacity.

In summary, to answer your question: There is a situation and controller based threshold, at which saturation will be reached. Controllers are trained to anticipate this threshold and make their supervisor aware of the situation beforehand, so that measures can be taken. There is however no fixed numerical maximum, unless specified in the ARTCC/ACC's operating procedures.

"The minimum radar separation in TMA sectors and upper sectors can be either 3nm or 5nm." -- And there I was, wondering for a couple of seconds what kind of separation 3-5 nanometers would be (something with the radar waves? huh?), before the cerebral cortex kicked in and whispered "nautical miles, you noob" into my ear. :-D

@DevSolar You are correct however, it's spelled NM and not nm. Corrected, thanks.

I am sure that in Europe there is a fixed maximum, based on flight plans. I believe the limit is 35 per hour for en-route segment. Beyond this flight plans are rejected by the flow control system and the dispatchers must try alternate route or accept delay.

@JanHudec That would be a CFMU capacity limit, not a per controller / per sector limitation. Aren't these limitations rather in place to control airport arrival capacity?

@SentryRaven: They are CFMU capacity limits. But (IIRC) they also limit sector capacity to limit peak controller workloads and frequency congestion.

@JanHudec I'll give this some research and will see if I can incorporate this into my answer. Thanks for the info.

Chuckling here, as this is a hotly argued topic in controller circles. There is no direct official number. One airplane can be all a person could work(major emergency lots of coordination, etc.), or they could work 20+ and not break a sweat, it heavily depends on the nature of what's occuring and the staffing at the facility, the positions that are designed at the facility(various sectors at a tracon, where there's designated airspace for the position and frequency).
During the design and course of life of facilities, they constantly evaluated the positions they need during peak traffic times, to slow times, and the required staffing levels for those positions. Sometimes all you need 99% of the time is two positions, so that's what they'll aim to staff for, other times, based on history and operators at the airport you can get a good idea when your peaks and valleys occur and plan position distribution accordingly, with the staffing you have.

"it depends" is not really an answer, unless you can provide some concrete details, like how many airplanes per hour, which way the runways are facing, and of course the biggest factor: WEATHER

@rbp None of those factors really make the answer any more specific than "it depends". You can factor all of that in and then you have one pilot whose head isn't in the game and the controller is saturated trying to deal with them, so the answer is "ONE airplane, with a pilot who needs to be beaten sensible".

@rbp "It depends" is the best answer you will get, because it does truly "depend" an many variables. Pilot awareness, controller ability, weather, neighboring controller ability (yes, the controller who handled the aircraft before you could have really muddled things for you. Maybe he/she was a newb or trainee and his/her monitor wasn't paying close attention) and many, many other factors. Air Traffic Control isn't a "science"... it's a skill honed from year's (not hours) of experience. "Concrete details"? There are none! Nothing in ATC is set in stone. Circumstances change every second.(cont)

@rbp ... As a controller you develop the skills to adapt with the changes and keep the skies safe. Finally... "which way the runways are facing" has absolutely no bearing whatsoever. And as for "weather"... modern radar filters out weather... only moving targets (aircraft) show up on radar.

There is no limit, really. The question is not whether the controller would "start making mistakes", it is how much attention would the controller give to each plane, which just grows less and less the more aircraft there are.
Even if the tower goes completely dark, the pilots will self-organize and land themselves. The controller is just there to make the process easier and safer.
Sometimes controllers do ignore you when they get busy with something else and what happens is you end up flying really LONG downwinds, so by the time the controller gets around to you, you turn onto a 5-mile final or something like that. If the controller completely blows you off, you can leave the pattern, do a U-turn, come around and re-enter the pattern to try again.
At a big airport with a lot of commercial aircraft, if the controllers started to go AWOL the pilots would probably just stack themselves up on the instrument track, and even start landing themselves if the tower became totally unresponsive. To do this, they just tell the other pilots where they are and their position in the queue ("Lufthansa One Echo Echo downwind for two four left, number three behind the Embraer", etc).

@Kuya Not a very specific comment. Instead of throwing insults around, I suggest making concrete statements concerning what you object to in my answer. Or better yet, make your own answer.


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How do airline pilots relieve the physical stress and discomfort of sitting for long periods of time?
Airline pilots are required to sit in the cockpit for quite a considerable amount of time during their day. For example, during the preflight, climb and descend portions of the flight, there are many events going on in the cockpit that requires both pilots' attention. The amount of time they are required to spend sitting in the cockpit is, surely, longer than that of a passenger on the same flight.
How do they relieve the physical stress/discomfort and other physiological issues associated with sitting for a long time? For example, during cruise, is it normal for one of the pilots to unbuckle the seatbelt, get up and stretch his legs in the cockpit? Do they do some simple exercise for a few minutes during the turn around?
Note: This question is not about how pilots deal with the mental stress of boredom in a long flight. This is about how they deal with the physiological discomfort associated with remaining in the sitting position for a long time.

Related

Related: How do long-haul pilots cope with boredom?

I'm putting this as a comment since I retired in 1999, and post-911 the rules may have changed. Anyway, my practice was to get up every couple of hours and at least go into the upper deck (747), and I'd always take at least one tour around the main deck cabin. If the flight was 10+ hour flights I usually do two tours.

"The amount of time [the pilots] are required to spend sitting in the cockpit is, surely, longer than that of a passenger on the same flight." Well, the passengers are usually forbidden from sitting in the cockpit at all. *baddum-tsh*

More seriously, though, I'd say that pretty much all passengers spend essentially the whole flight sitting down, except for trips to the bathroom. Especially given that there's a relief crew on really long flights, I'm not convinced by your reasoning that the flight crew have to sit more than passengers.

@DavidRicherby the pilots have to preflight, and usually when the passengers are deplaning, the pilots are still finishing their checklists or documents (my observation as a passenger). And they may do multiple trips a day.

I was on an EMB-145. The longest flight we usually had were 3.5 hours so my experience doesn't compare to Trans Pacific routes. As a crew-member I could get up to use the restroom, but there wasn't enough room to stand on the flight deck. You learn to sit different ways (one leg under you) to makes adjustments. Then the other leg under you later and so one. Some sort of seat Yoga I guess you could call it. My strategy was to walk, walk, walk, and stay off the plane as long as I could between turns. Your body adapts to the environment after awhile regardless of your body being in great shape or not.

I piloted 4 hour flights without much physical issue. There was noticable mental fatigue as they were single pilot operations with a complex flight plan, having a copilot will help a lot with that part.
Pilot seats are much better than passenger seats, both in basic shape and adjustment. Pilots also have rudder pedals and many hand controls so there is inherently more movement than one will get as a passenger, individual limbs and leaning this way and that. When I first started pilot training I also had to start exercising because I actually had fatigued muscles after two hours of flying maneuvers.
Everybody, both crew and passengers are required to be seated upright with seatbelts during taxi takeoff and landing phases.
In cruise with two pilots one pilot may leave their seat for several minutes, depending on altitude the remaining pilot may be required to wear an oxygen mask to reduce risk if an emergency occurs. Regulations change with the type of operation and country, but some operations require at least 2 people in the cockpit at all times though this can be one pilot and one cabin crew.
On very long flights there will be 3 or 4 pilots on board with 2 flying and they may rotate about 3-5 hours. The aircraft equipped for such very long flights also have a room with beds for both pilots and cabin crew. The exact length of flight for adding a third pilot and shift rotation detail is dependent on the regulating country.


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Why does the MiG-25 have silver-coated panels?
This is about the Mig-25. This documentary on youtube, @10:03, says:

Special insulating panels had to be fitted to protect the area around the engines from overheating. The panels were silver-coated. Five kilograms of silver were used in their manufacture.

My question is, why? What does silver-coating do exactly? AFAIK you still need some kind of cooling, either air or liquid, or else the heat flux will steadily raise the temperature to the failing point.
Wikipedia lists the thermal conductivity for silver and copper as 429 W/(m·K) and 401 W/(m·K) respectively. It is only a slight difference and I can't imagine why you would absolutely need that slight difference for a massive increase in cost. Plus I'm pretty sure silver (and gold) are a lot easier to melt than copper.
The only "special" thing about silver, that I know, is that it's highly reflective and therefore is used in the mirrors of superindustrial strength telescopes. I cannot imagine you would need that inside an engine, as virtually all the heat comes from conduction via the hot engine gasses, not radiation.
Edit: The silver could be part of some silver alloy. It would still have to be a coating of this alloy.

Reflectivity, maybe? I have no hard data to support this but my first instinct is to check wether a silver panel would reflect more incoming radiation than a copper one, thus reducing one heat transmission vector. Conductivity only matters after the energy has been delivered to the material.

The emissivity of polished silver is very low, the lowest of any metal. Hence, a silver-coated hot object radiates energy very weakly in the infrared (and absorb radiant heat weakly, too...).

Because they are very pretty--

As you have pointed out yourself, the Silver is there because it is highly reflective. The panels around the engines were coated with silver to prevent the heating of the fuselage around it. According to this document,

The engine bays each incorporated heat shields coated with a 30-micron layer of silver (5 kg/11 lb per  aircraft), which absorbed 5 percent of the heat and represented a more cost-effective solution than gold or rhodium, though these  metals were tested.

The panels basically trapped the heat within the engine bay, which is then cooled using boundary layer bleed air from drain slots between the air intake sides and airframe sides.

Your source says the silver absorbed the heat, whereas your first paragraph talks about reflection. As per my numbers, silver is an even better conductor (of heat) than copper, so it would have a very poor heat capacity and thus not good at absorbing large heat for little change in temp. I will nonetheless make an edit to my OP because I just realized the silver could be part of a silver alloy with who-knows-what properties.

@DrZ214 You should read that as "only five percent.

With fire, heat transfer via radiation is usually very significant. The hot gasses have fairly low heat conductivity, and can be kept off the walls by suitable flow pattern, but give out a lot of (visible, even) radiation.

The description suggests the silver coating isn't exposed to the hot gasses anyway. It is on the fuselage structure facing the casing of the engine. Convection across this gap is limited by flowing cold inlet air through it, but there would still be a lot of radiative heat transfer and that has to be limited by using a reflective coating.


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How much weight does a thrust reverser add?
How much weight does a thrust reverser add to an engine?
Let's take the CFM Leap 1B as an example, which powers the new version of the Boeing 737. This engine can produce up to 130 kN of thrust for takeoff, and has a dry weight of 2.78 tons. I could not find how much weight is the thrust reverser system. Closest thing I found was this FlightGlobal article which at least talks about it, but doesn't give numbers.
One purpose of this question is to compare it to old-school drag chute system. I will open a separate question on that.

@ymb1 In my experience, things like that usually get criticism for being two broad. Usually someone recommends them split into 2 separate questions.

The detailed weight of the components of the Leap 1B are elusive to find at the moment. There is statistical data available in pre-design books, such as Synthesis of Sub-Sonic Airplane Design by E. Torenbeek. Chapter 6.6.1 deals with thrust reversers, and mentions that the weight is considerable: between 15 and 20% of the bare engine weight, with the higher region being for high bypass engines like the Leap 1B.
Wikipedia lists the weight of the 1B as 2,780 kg. If we take the mid region of percentage due to improved technology since the book was written, the resulting guesstimate for the weight of the 1B thrust reverser is 0.18 * 2780 = around 500 kg. Plausible if we consider the complexity of the system.

The book also mentions an alternative means of thrust reversal for turbofans, the same one as used for turboprops: fan pitch adjustment, developed by the Dowty Rotol company early enough to be mentioned by the book. This mechanism weighs about half of that of the thrust reverser, amounting to about 250 kg, and has of course the advantage of being able to optimise blade pitch during cruise and take-off. Rolls Royce has announced plans for adjustable fan pitch for the next generation engines.

It obviously depends on the engine and airframe involved. For example, in case of Hawker 700, the aircraft with thrust reversers,

... has 248 pounds less useful load than a Hawker without reversers.

As the Honeywell TFE731 used in the Hawker weighs around 734 lb, this works out to about 17% of the engine dry weight. The thrust reversers seem to be classified as a structural component.
In case of present generation high-bypass turbofans, this value will be on the higher side due to various other factors like acoustic liners for meeting noise requirements (which the TFE31 doesn't). So, 15-20% appears to be extra weight due to the thrust reversers.


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Has there ever been a seaplane with inflatable airbags rather than traditional pontoons?
Traditional pontoons are big and cause a lot of drag. It would be nice to retract them like normal landing gear but they are just too big.
Has there ever been a seaplane with inflatable airbags instead? They way I imagine it is a lot like normal landing gear, with lowering struts from the wings or belly. But instead of wheels, it has a wound-up airbag that's unrolled and inflated.
I think this would save a lot of drag and weight, and I'm a little surprised that this apparently doesn't exist over the 114 years or so of airplane history. Is there something unfeasible about this concept? I suppose getting propeller clearance over the water is the biggest concern, but I would think slightly long legs on the landing gear would be sufficient and well worth it to save all that weight and drag from those big pontoons.
Edit: This is for the really small planes.

I would think the stresses would be fairly high and I dont know of any off the bat but there have been helicopters outfitted with them.

(source)
On the drag front, this is only really a problem for smaller sea planes (C172, Caravan etc.). On the large side of things when you want to reduce drag a belly land design is used like in a Grumman G-21 or even as far as the worlds largest airplane the Hughes H-4 Hercules.

Yeah a belly-lander works for bigger planes but the thing I was envisioning was a small, single-engine piston prop plane. A belly-lander probably won't have enough clearance for its propeller.

Is that a ... duck-style walking helicopter?

@DrZ214 there have been some single engine belly landers over the years like the SeaBee

The Goodyear Inflatoplane was used with a hydroskid so technically one can say that there has been at least one plane with inflatable floats.  There also several ultralights that use soft floats, too.

Life just got a bit better knowing that inflatable planes exist and could fly for hundreds of miles.

Sounds like the Inflatoplane was a reasonable option for recovering a downed pilot, but useless for other troops who didn't have flying skills.

"ATC, we've lost cabin pressurization. Request emergency descent to FL 0 at 9.8 m/s^2"

There was an attempt made during the 1950s to build a sea-plane fighter jet with retractable water skis (the Convair F2Y Sea Dart). The basis for the idea was that supersonic fighters were bigger and heavier than all previous fighters, and the US Navy was worried that the carriers would be too short for safe takeoffs and landings.
With a seaplane there was no such worry; the aircraft could simply be lowered into the sea, turn into the wind and take off, and be hoisted back onto the carrier after it had landed.

Apparently, the F2Y is the only seaplane ever to have gone supersonic.

The stresses on an inflatable float at take-off and landing would probably have been too high for the materials of the 1920s and 1930s, when seaplanes and flying boats were economically and militarily important. Another approach was invented by the Blackburn Aircraft Company in the UK: a retractable float.
Their B-20 experimental flying boat avoided having the deep hull that would have been necessary for propeller clearance by being able to lower its whole underside a few feet. This did actually work, and the aircraft's crash was due to an unrelated flutter problem.

Bell did some experiments with a hovercraft setup on a Lake LA-4. If you do a Google image search for "Bell Aerosystems air cushion undercarriage", you'll see pictures of it, as well as a DHC Buffalo and a Soviet attempt.
https://goo.gl/images/uVUFfA


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In WW2 aircraft, where were gun cameras mounted, and did they suffer performance penalties?
During WW2, some aircraft had gun cameras that activated whenever the guns fired, so that people on the ground could evaluate performance and help with kill ratios and other statistics. These were actual video movie cameras, using film.
I want to know, where were the guns cameras mounted? And how much performance penalty did they incur, in terms of weight and drag added? I cannot imagine that they were actually inside the cockpit, because movie cameras back then were big things.

"movie cameras" not "video cameras"

Video is an electronic medium...

@A.I.Breveleri and J... My mistake, edited.

It was a small 16mm film camera usually mounted, in single engine fighters, in the inboard area of the wing, within the leading edge behind a little window (the P-38's is also about the same location between the center pod and left engine) or in the nose in twins.
Look carefully at a lot of gun camera film on something like a P-51 when the sun is lighting up the prop from behind and you can see that the camera is viewing through the lower left quadrant of the propeller arc, being just a couple feet to the right of the left side wing guns.  Most fighters only had up to 30 seconds of continuous firing time in ammunition, so it didn't need to have a really large film supply.
On some systems the camera could be set to run only during firing or could be run independently and there was a little flag that appeared in the upper left corner of the film image and lifted out of the way when the guns were firing and dropped into view then they weren't.
A lot of pilots started to do away with tracer ammunition when lead computing gyro gunsights started to appear in 1944, so often the little flag is the only way you can tell the pilot is firing other than bullet strikes (and vibration from the guns sometimes) when you watch gun cam movies where no tracer is being used.
The weight penalty was negligible, only weighing a few pounds, and the drag penalty was also negligible, being buried in the leading edge behind a clear panel, like a small landing light.

Does your first sentence apply to all aircraft, or to a particular country's air force?  It's not clear how inclusive you mean to be.

Most of the details would apply to US/UK fighters.  German fighters similar as per Peter's answer. Not quite sure what the Japanese and Soviets did.

German fighters used the BSK 16 (Ballistische Schussmess Kamera [Ballistic Shot Measurement Camera] 16mm) which was mounted in the wing root in case of single-engine aircraft. Twins would carry the camera usually in the fuselage nose. It contained black&white film material for a maximum of 200 seconds of filming.
Activation was either together with the guns or by a separate switch. Another switch would control the heating element for the camera and a control light in the cockpit would indicate camera operation.
Since the cameras were fully enclosed within the structure, performance was only affected by their additional mass.

Robot II camera in the wing leading edge of a FW-190 A3 (picture source)

BSK 16 being mounted in the nose of a Bf-110 (picture source)


text:
The ATC is unable to provide radar service to pilots, what's the standard way to inform this?
Nowadays, ATC provides radar services to pilots, such as: vectors and surveillance, however, depending on the radar status, it can be out of service; on initial call the controller will inform the pilots about this issue, please, what's the right way to say this, using standard phraseology?

Please add a jurisdiction, as some countries (especially the UK and the USA) handle this quite differently from most of the world

Without checking the Controller's Handbook, what I hear most often are two things:
a. Standby and remain clear of class [b, c] airspace, for VFR operations.
b. (surveillance) radar services not available, squawk xxxx, report yyyy
c. Radar out of service, N1234, radar service terminated.
An example of b was when going to an airport near DCA, radar was out of service.  The controller handled my flight but relied on talking with a controller from Baltimore. This was a few years ago, and I now understand that the remote radar can be transmitted to other controllers taking a remote controller out of the loop.
The ATC Handbook is FAA JO 7110.65W, https://www.faa.gov/documentlibrary/media/order/atc.pdf
Radar can be limited due to equipment outages, and also the display available to the controller.  For example tower displays are for orientation and not certified for separation and other services.
The order states that controllers may advise that:
PRIMARY RADAR UNAVAILABLE (location)  or
RADAR SERVICES AVAILABLE ON TRANSPONDER EQUIPPED AIRCRAFT ONLY
Since there are many conditions for radar not being available and since an aircraft can be in various states (VFR/IFR, approach, visual approach, etc.) it would be best to consult the Order for the recommended phraseology.  It is noteworthy that CONUS radar coverage has improved since the Order, and as a result there is often backup coverage for many locations which could influence services which can be offered.
Finally, operationally ATC still has local and regional variations, which may influence the options and corresponding phraseology utilized.

In many parts of the world, "radar service not available."

if it’s a terminal radar then the ATIS would state that the airfield is operating procedurally. If it’s an enroute radar then the controller would probably tell you when you first called by stating that they’re operating either ‘surveillance only’ (IFF) or ‘procedural control’ if both are out. They’d then ask you for estimates for various fixes.  A lot of places which don’t have radar coverage full stop don’t bother telling you and just ask for estimates so it’s implied there no radar.

Special thanks for your answer.

The controller would probably just say something simple like “radar is out of service”.


text:
On radio telephony, is there any difference when using ALTERNATE and DIVERT, to change my destination airport?
If my destination airport is closed, or if I decided to land on a different airport I have requested on my FPL, should I use: Request to DIVERT to or ALTERNATE to?

"Alternate" is not a verb.1. You don't say "I am alternating to...". "Divert" is a verb. You do say "I am diverting to...".
If you are flying to airport A, but you have a backup plan that if the weather is bad you will land at airport B, then B is your "alternate" airport. If there is a weather concern at A you might tell ATC: "My alternate is B", meaning that if the weather gets worse you will go to B, and letting ATC know in advance that you might require a clearance to B. As soon as you decide to go to B, whether because of weather or because you feel like it or some other reason, then you say "I am diverting to B".
Note 1: There is a verb "alternate", but it has a completely different meaning and isn't relevant here.

Also note that (at least in the USA) there is no requirement that you divert to your planned alternate. You certainly may, but if another airport makes sense instead that's fine too!


text:
When should I use "cross" and "pass" on radio telephony?
Talking about "vertical" plan (altitudes, flight level) and "horizontal" plan (positions, way points), according to the standard phraseology FAA/ICAO, is there any difference, in the usage of, between TO CROSS and TO PASS?

When related to a significant point, there is no difference between pass and cross. For altitude/FL only pass is used.
The phraselogies used by ATC is described in ICAO Doc 4444 (Air Traffic Management / PANS-ATM), chapter 12, phraseologies. The document explains the meaning for ATC, therefore to be understood and used by pilots.

12.3.1.2 LEVEL CHANGES, REPORTS AND RATES

EXPEDITE CLIMB (or DESCENT) [UNTIL PASSING (level)]
AFTER PASSING (significant point)

12.3.1.4 TRANSFER OF CONTROL AND / OR FREQUENCY CHANGE

AT (or OVER) (time or place) [or WHEN] [PASSING/LEAVING/REACHING (level)] CONTACT (unit call sign)
  (frequency)

12.3.1.10 ADDITIONAL REPORTS

REPORT PASSING (significant point)
REPORT PASSING (three digits) RADIAL (name of VOR) VOR

12.3.2.3 MAINTENANCE OF SPECIFIED LEVELS

MAINTAIN (level) UNTIL PASSING (significant point)
MAINTAIN (level) UNTIL (minutes) AFTER PASSING (significant point)

12.3.2.4 SPECIFICATION OF CRUISING LEVELS

CROSS (significant point) AT ( or ABOVE, or BELOW)
CROSS (distance) MILES, (GNSS or DME) [(direction)] OF (name of DME station) OR (distance) [(direction)] OF (significant point) AT (or ABOVE or
  BELOW) (level)

12.3.2.8 SEPARATION INSTRUCTIONS

CROSS (significant point) AT (time) [OR LATER (or OR BEFORE)]
ADVISE IF ABLE TO CROSS (significant point) AT (time or level)

12.3.3.1 DEPARTURE INSTRUCTIONS

AFTER REACHING (or PASSING) (level or significant point) ( instructions)

12.3.4.12 TURN OR CLIMB INSTRUCTIONS AFTER TAKE-OFF

AFTER PASSING (level) (instructions)

12.4.2.3 PARALLEL APPROACHES

YOU HAVE CROSSED THE LOCALIZER (or GBAS/SBAS/MLS FINAL APPROACH COURSE)

If another wording is used in some country, the differences must be explained in the country AIP, at section GEN 1.7. For USA (FAA AIP), Doc 4444 differences are found at GEN 1.7-23. There are none related.


text:
When using the phonetic alphabet, for airways, should we say Uniform or Upper?
Listening some RTs, I heard ATCos reporting airways, for example: UL65, UPPER LIMA 65. But the phonetic alphabet says UNIFORM. Why do they say like this, please? Is there any manual in which we can study these differences?

This sounds a lot like how "runway 19L" is pronounced "runway one niner left" instead of "runway one niner lima". In this case, I wouldn't say that the letter "L" is being pronounced as "left" instead of "lima"; I'd say that the phrase "runway 19L" doesn't end with the letter "L" at all, but rather with the word "left", which happens to be written the same way as the letter "L".

If there were an airway UU65, presumably that would be "upper uniform six five", not "upper upper six five".

Did you used to go by Tanner Swett?  Just curious...

@MichaelHall I sure did. My username is still Tanner Swett on all other Stack Exchange sites, but it's Terran Swett on this one. If you'd like to know the reasons, send me a ping in https://chat.stackexchange.com/rooms/12036/the-hangar.

When I was being taught radio procedure we were told that if the letter stood for a word you should always say the word it stood for, not the alphabet word. So "AIR TRAFFIC CONTROL" not "ALFA TANGO CHARLIE". It  no longer and less liable to error.

@JimyPP is correct on the use of Uniform.
In this case (I assume you are listening in Europe) there is such thing as an Upper airway. So the controller was correct in his phraseology

All airspace above FL195 is class C controlled airspace, the
  equivalent to airways being called Upper Air Routes and having
  designators prefixed with the letter "U". If an upper air route
  follows the same track as an airway, its designator is the letter "U"
  prefix and the designator of the underlying airway.

I'm not really sure what the controller meant by "Upper". The "U" in UL65 might already stand for the word Upper, so he used the entire word instead of the one letter abbreviation.
The phraseology for the letter U is indeed "Uniform" as you can see on the specification of the NATO phonetic alphabet. There is no reference to the word "Upper" and only "Uniform" is correct.

Looking at https://en.wikipedia.org/wiki/Spelling_alphabet,I don't see "Upper" as part of any of the phonetic alphabets listed.

"Upper" doesn't mean "U" -- it means "at higher altitude".

Following that same logic your name isn't Jimy, instead it's Juliet.

It is important to understand the reason for the phonetic alphabet.  It is not intended that plain language words should be abbreviated, then re-expanded using a phonetically pronounced first letter as a code word substitution for the original word.  Rather it provides a means to spell out a word in cases where communication is difficult.
If a controller couldn't hear well and misunderstood the word "upper", saying "uniform" by itself would probably not help unless the context was very clear.
For example, an exchange where the phonetic alphabet is useful might go something like this:
Controller:  "Say again, did you mean 'udder' like the udder of a cow?"
You:  "Negative, I spell - Uniform, Papa, Papa, Echo, Romeo."
Whenever a plain language word exists you should generally use it first, but spell phonetically as necessary to clear up any miscommunication.
The caveat to this is when the phonetic version is in more common use.  I am not actually familiar with the term "upper" as it pertains to an airway, but in the US the low altitude airways are referred to as "victor" airways.  I am guessing that originally the "V" may have been for VFR, but nobody seems to know or care, or to call them anything else.
If the convention is to say "uniform" instead of "upper" (even if that is what it originally meant...) it is generally easier to follow convention to avoid confusion.  In the case cited in the question though, it seems that the plain language word is being used.


text:
How do I say these situations, according to the runway's status?
There is an accident on the runway, for example, the aircraft is disabled on it, so, the runway is_________.
The runway is flooded, or there is oil spill on it, so, the runway is______.
Closed? Unserviceable?

In the US, you would use "closed". From the FAA's Pilot/Controller Glossary:

CLOSED RUNWAY− A runway that is unusable for aircraft operations. Only
  the airport management/ military operations office can close a runway

And this is part of the example ATIS broadcast from the same document:

Left approach in use, Runway Two Five Right closed, advise you have
  Alfa.

I don't know if ICAO uses a different term, but "closed" is probably going to be clear to most pilots (and non-pilots, for that matter).

Occasionally I'll hear over ATIS "Runway XY closed for snow removal" or painting, or whatever, they don't have to explain it, but at my local airport they run through the airport NOTAM's on the ATIS.


text:
How does a combat aircraft handle the recoil force of a mounted gun?
How is the recoil momentum distributed or countered for smaller aircraft or drones while using a mounted gun? Is there any hydraulic mechanism to counter it and how it is distributed across the entire body of an aircraft?

How big of a gun are you talking about? 75mm gun on B-25s?

about c13 with 103 caliber or for a smaller aircraft with sub meachine gun

if there were a hydraulic buffer system it's more likely be a part of the gun sub system not part of the aircraft.

In case of combat aircraft, the guns are hard mounted on the fuselage (or wings, for that matter) so that the recoil force is distributed throughout the body. In this case, the large aircraft mass acts to reduce the effects, though if the gun has too much recoil, it can cause damage to the aircraft. For example,

The MiG-27's GSh-6-30 cannon didn't prove particularly useful in practice. It was an impressive weapon in principle, ..., but the recoil -- about 5.5 tonnes (6.05 tons) -- still had a tendency to inflict damage on the aircraft. ... Landing lights almost always broke after firing,

In case of smaller aircraft or drones, you can chose a gun with lesser recoil. Or the drone (for example) could be programmed to fly back to its original position as a way of 'absorbing' the recoil.
Another way is to mount the gun on stabilization platform, which makes sense only if the gun is quite small. A few such systems exist, which usually use robotic stabilizers to reduce the effects of the recoil due to the gun.

@CGCampbell Drone shoots once -> Is knocked out of position by uncompensated recoil -> Automatically flies back to firing position. While not very hard to do in practice, this idea only works if drone cannot be damaged or lose stability enough to crash due to recoil. Also there's the issue of the operator not wanting the (possibly significant) delay on the second shot.

The force of the recoil is distributed into the airframe in the same way that engine thrust is. Recoil is nothing but impulse thrust, like what happens inside a piston engine which is exploding gas propelling a piston mass as well.
So structurally, there is no special wizardry required, everything just needs to be strong enough. The main issue here is making sure that the aircraft can still be flown while the gun is doing its job, and that the aircraft is still pointed more or less in the intended direction, as this answer addresses.

The firing of a forward firing cannon can generate thousands of pounds of reverse thrust. The use of shock absorbers in the gun mounting has the effect of reducing the peak recoil forces which might damage the airframe, but it does not reduce the average recoil force/thrust or the total impulse imparted to the aircraft over the time the gun is firing.
If the weapon aiming system in a drone or UCAV is capable of improved accuracy relative to a manned aircraft then a high rate of fire might be rendered unnecessary, which would reduce the impact on the aircraft's flight performance and would also mean that the gun itself could be lighter for a given calibre.


text:
How to calculate the fuel flow using the thrust specific fuel consumption?
Using the following parameters:

Static Thrust : $T_0 = 12 KN$
Thrust specific fuel consumption: $C_T=0.7 N/NH$

I know that the fuel flow is linked to thrust with the following formula:
$F=C_TT$.
And I need to calculate the fuel flow in Kg/s.
I started by converting $C_T$ in Kg/Ns:
$0.7 N/NH = 0.7 \frac{1}{9.80665} \frac{1}{3600} = 1.9828* 10^{-5} \frac{Kg}{Ns}$
Then I multiplied this value with the thrust:
$F = 12000* 1.9828* 10^{-5} = 0.2379 \frac{Kg}{s}$
However this does not seem to be the correct answer. What am I doing wrong?

Your units look wrong. TSFC should be g or kg per N and h to begin with. Your conversion should not be needed. If you use the same unit for weight and thrust (like lbs in Imperial Units), you get the specific impulse which is popular in rocketry, but unusual in aviation. The number of your TSFC looks like the TSFC in kg/Nh for a low-bypass engine. Maybe you should check the source of that figure and use it without the conversion.

As Peter Kämpf said, the units should be in kg per N per second/hour.
In your case assuming it's a typo, and assuming the formula is $\text{C}_\text{T}$ = 0.7 kg/h per Newton.
Then in static condition,
Fuel flow $= 12 \cdot 10^3 \cdot 0.7 \cdot \frac{1}{60} \frac{kg}{s}$
gives 140 kg of fuel per second. Seems correct.
As a side note TSFC is not a fixed value but a variable of velocity as well. So have to make sure this CT is for static condition.


text:
Where can I find airport diagrams from airports all over the world?
I am trying to build a database of airport diagrams (PDF documents). For the US, the FAA seems to be the best source. Are there any other free sources for Europe, Asia, etc...
Also the data needs to be reliable.

This is likely the same answer than Where can I get IFR charts for throughout the world?, in the national AIP.

For Europe, the European AIS database (EAD) would be the best source.


text:
Would it be possible to use a magnetron beneath glider plane to generate its own thermals?
Would it be feasible to install a series of magnetrons or something else on the underside of a gliders fuselage and wings in order to heat the air beneath the glider and ultimately cause the glider to obtain high altitude flight or obtain flight when thermals are not available? If hot air rises would you theoretically be able to artificially heat the air beneath a glider in order to achieve high altitude flight?
I was watching videos about gliders and I noticed that thermal air pockets are often required to achieve altitude gain. I'm a dumb guy so excuse me if this is a ridiculously dumb question.

That seems more a question of basic physics than an aviation one: How much power would be required, including to lift the mass of the additional equipment?

A propeller is much more efficient.

This would not be feasible.  First of all electromagnetic radiation emitted by magnetrons would heat up the water vapor in the air and not necessarily the air itself.  Molecules must have a dipole for EM heating to work.  Second it is not just the heat, what really creates the lift is the moving air upwards.  If you heat the air underneath the airplane that doesn't mean you will make the air move.  Thermals are typically less effective when close to the ground.  Thirdly, finding thermals on your own is part of the sport.  I think that generating your own thermal would defeat the concept of the sport.
Also gliders don't have to completely rely on thermals to stay up.  Ridge Lift and Wave Lift can be used in mountainous areas where the lift is generated by a moderate wind slamming perpendicular to a mountain ridge forcing the air up.


text:
What are the difficulties of landing on an upslope runway?
On runway like the one in Courchevel Altiport, how difficult is it to land? what is diffirent in the aircraft landing configuration when landing on an upslope runway vs normal runway?
EDIT:
Thanks for the answers guys, I didn't know that the airport had a level "touch down" point. still I am curious what should a pilot do (regarding air speed, pitch, flaps ...) if the runway itself was 10% upward (no level parts)... would the plane be in a "climbing-like" configuration? what about speed?

This video shows that the approach end is relatively flat and its only the middle part that is at a slope. The approach is probably pretty much the same, except you can't go around so you have to stick it the first time.

Actually regarding *takeoff guys, at Courchevel do you go up or downhill, or are both possible?  In theory is it easier or is it harder to take off if the runway slopes down versus normal flat takeoff runway? What about one that slopes up versus normal flat takeoff runway?

@JoeBlow In the case of Courchevel and Tenzing-Hillary in Nepal, take-offs and landings are only allowed in a certain direction. Take a look at this video to see what the pilot see's. Imagine trying to take-off uphill, not only do you have the slope of the runway to deal with, but the unforgiving mountain behind it. It is always harder to take off uphill and easier to land uphill.

@RonBeyer - got it, thanks!

Please don't edit your question to add "thank you" or follow up questions. Accept the most useful answer to say "thank you" and ask different questions for any follow up, referring to this question if it helps to give context.

This is the landing configuration at Courchevel, the runway is not level at all at the threshold. This snapshot is extracted from the video of the airfield certification preparation. The flare out is done without decelerating. The aircraft approaches at 5% the runway which is at 12.%, that a large total angle of 17%! The video describes the traffic pattern with written indications both in French and English.  I suggest you reactivate your question with this information.

Courchevel does not have a level touch down point. The touch down area has a slope of 12.5%, as compared to the steepest runway slope of 18.66%. See the airport diagram.

I never landed at Courchevel, but did some aerobatic training in Zar in the Giant Mountains of Silesia.
What I learned was:

A proper approach looks steeper than normal because the field inclination is steeper relative to the plane's attitude.
You need to flare sooner for two reasons:

 The sink speed relative to the rising ground is higher than normal, and
 The amount of pitch change needed to flare is larger.

Even with airplanes which have a strong ground effect (and where too fast a touchdown speed will normally result in a very long float) the flare was short, as was the rollout distance. Don't let speed bleed off too early, but stay on your approach speed until you are low enough to flare.
Airports with slope sit on the sides of mountains. In many cases, the
approach is already over rising terrain. When landing with a
headwind, the wind will create a downdraft along the approach so the
sink speed during the approach will be higher than normal. For glider pilots this is the biggest danger - once you are too low, you will hit the ground short of the runway.
Most inclined runways show a variation in inclination along their length. This means that the relative sink speed and the necessary pitch change for a successful flare will vary with the touchdown point. Stay alert, no landing is routine!

The landing configuration and approach speed were not different from that on regular airports with level runways. Different was mostly the height at which the flare is begun. Also, at first I needed getting used to staying on my approach speed until I was low enough to flare - you need more energy to keep the airplane flying until it is level with the ground (i.e. climbing uphill!), so the final approach and flare must be executed precisely for a good landing.
When I saw the runway at Zar for the first time I thought the location is sheer madness. After a few landings I learned to appreciate the benefits: Very short roll-outs and planes would land uphill only, so they come to a stop where the (downhill) take-off run could begin. But the approaches need to be precise (we did mixed motor and glider flying) especially with gliders if you want to keep your fellow glider students happy.

For Courchevel, see this instructional video. The angle between the glide path and the runway is 17% at the threshold.

As far as landing in a up-sloped runway is considered, the pilot will make a lower approach if not careful as he/she may consider the ground before to be sloping up as well. From flytime.ca:

When a runway is upsloping, the pilot thinks that the runway continues on an upslope from the terrain before it, hence thinking the terrain in front of the runway is upsloping as well.   The pilot will judge their altitude as too high, because they perceive the terrain continues on an upsloping, positive angle towards the runway  and will consequently plan a low approach that can cause landing short of the runway.

Image from flytime.ca
Another thing to note is that the landing roll will be reduced (on the other hand takeoff roll would be increased, if takeoff is on uphill direction; else, it's reduced). For example, in this airport, the actual landing point is level- shortly after the aircraft touches down, it will start traveling uphill, and the landing roll will be shorter. One (passenger) describes the landing as:

During the approach we were below the runway and climbed up to it to land. After touchdown, we slowed down very fast due to the upslope. Very different than the normal runout after a landing.

Of course the location of this particular runway means that the landing has to be done correctly the first time around.

Its not the upslope at Courchevel which makes landing there hard - its the big whopping cliff at the end of the runway. There is no go around so its a one-shot deal.
In general though, up sloping runways give two effects that I can think of

The runway on approach would look different to a flat runway, this might have the effect of making an inexperienced pilot think they were too high.
The landing roll would be shortened by being on an upslope.

Tenzing-Hillary airport at Lukla was also always said to have no possibility to go around, until this video clearly proved it's not true. The terrain around Courchevel looks quite similar, so going around is likely possible from similar point.

@JanHudec I think the pilot of that otter may have needed a change of clothing. I'm going to bet he didnt recommend that course of action routinely too.

Courchevel is one of a few airports that has such a gradient but ill talk about it a bit more generally. Ron makes a good point in his comment that the plane actually touches down on a fairly level part of the runway then uses the up slope to slow down. With this in mind you must consider a few things, for one your touch down point must be at the more level end of the runway. If you think you are not going to make that, GO AROUND. Due to the mountains and up slope a go around is going to be a Vx scenario to make sure you get the best angle of climb.
In a more general sense you are going to want to be a little more nose up if landing uphill on a runway. I fly into KDDH which has a 0.8% gradient (barely noticeable) but when landing up hill I am a bit nose high to keep it safe. Its not a terrible idea to keep back pressure on and relive nose gear loads but this should be done anyway. Unfortunately the planes I fly are not permitted on grass strips and Im still working on really nailing my landings so 0.8 is the steepest I have flown into as of yet.
This site has some interesting info as does this site

Is there any runway that has more gadient? that you have to be "flying up" to land on? I originally thought it would be that way in the mentioned runway, and was curious what knowledge is required to land on such runways

@RonanDejhero Courchevel has the record as the steepest at 18.6%, another harrowing one is Tenzing-Hillary in Nepal with a 11.7% grade but is considered the most dangerous airport in the world.

"Ron makes a good point in his comment that the plane actually touches down on a fairly level part of the runway". This seems to be a recurrent story. The aerodrome plate indicates 12% upslope for the first part of the runway, and this is clearly visible on this snapshot from this video of a qualification training specific for this altiport.

I landed many times at Courchevel. You can't just fly in. You need a training culminating in a permission to land there valid for 6 months. That should make it safe enough.
Sudden downdrafts can CFIT you just under the landing area.
Sudden updrafts can make you land way too far. That's why the pilot is VERY reactive on final.
Once on the ground you have to make sure you keep your speed up enough to make it to the top or you could get stuck midfield.

As you could see in the video that Ron Beyer linked (2. comment on the question) trying to land slows you down substantially as you are effectively gaining altitude when landing on an incline as you need to level yourselfes to the ground. This will make it harder for the pilot as he will have to adapt to this behauviour and land with just the right speed to not loose gliding or aproach from too low and not take to long to stop on a this short runway.
In conclusion it will take some practise to learn what speed is the best for this particular landing, but that isn't really different for other runways.
Another problem is the common ice due to the mostly cold wheather at 2000m above sea level, but that is not different to other airports in cold countries aswell.

What do you mean, stall your engine? Aircraft engines are not susceptible to stall from the moderate increase in pitch required to land upslope. The only thing I can think of would be if the aircraft went to such a dramatic attitude for sufficiently long enough to unport the fuel lines.